ParticleSystem.MainModule.startRotationMultiplier

Description

The initial rotation multiplier of particles when emitted.

This method is more efficient than accessing the whole curve, if you only want to change the overall rotation multiplier.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    private ParticleSystem ps;
    public float hSliderValue = 1.0F;

    void Start()
    {
        ps = GetComponent<ParticleSystem>();

        var psr = GetComponent<ParticleSystemRenderer>();
        psr.material = new Material(Shader.Find("Sprites/Default"));    // this material renders a square billboard, so we can see the rotation
    }

    void Update()
    {
        var main = ps.main;
        main.startRotationMultiplier = hSliderValue;
    }

    void OnGUI()
    {
        hSliderValue = GUI.HorizontalSlider(new Rect(25, 45, 100, 30), hSliderValue, 0.0F, 360.0F * Mathf.Deg2Rad);
    }
}